This invention relates to multilayer metal foil shields which have utility as heat shields and as acoustic shields.
Multilayer metal foil insulation has been used for many years, as illustrated by U.S. Pat. No. 1,934,174. Such metal foil insulation has typically been used in high temperature applications for reflective heat insulation. In those applications, the layers of metal foils are embossed to provide separation between the layers, and the stack of layers are protected in a container or rigid cover to prevent the stack of metal foils from becoming compressed at any portion, which would decrease the heat insulation value of the stack.
U.S. Pat. No. 5,011,743, discloses that multilayer metal foil insulation can provide enhanced performance as a heat shield when a portion of the multilayer metal foil is compressed to provide a heat sink area through which heat is collected from the insulating portions of the stack and dissipated from the heat shield. Such multilayer metal foil heat shields are formed from a stack of embossed metal foil layers by compressing portions of the stack to create the desired heat sink areas. The layers are attached to each other or stapled together to prevent the layers from separating. The heat shields and acoustic shields formed according to the disclosure of the U.S. Pat. No. 5,011,743 are typically compressed in the heat sink areas and cut to a desired pattern. Such multilayer metal foil heat shields do not normally have sufficient structural strength for stand-alone use in many applications. For many applications, the metal foil heat shields are typically attached to a structural support member or pan to provide a final assembly which is then placed in service as a heat shield or acoustic shield. The support members are typically metal pans or stampings or metal castings. Typical applications for such heat shield assemblies include automotive heat shield applications.
The disclosures of the above patents are incorporated herein by reference.
It is an object of this invention to provide a multilayer metal foil insulation structure which has sufficient structural strength to function as a stand alone unitary heat shield or acoustical shield without the necessity of the multilayer metal foil insulation being preassembled on a support member.
The multilayer metal foil structures of this invention comprise at least three metal layers at least two of which are metal foil layers having a thickness of 0.006 in. (0.15 mm) or less. It is generally preferred that the structures of this invention contain at least three layers of metal foil and more preferably will typically contain five to seven layers of metal foil. Preferably, the metal foil layers will be 0.005 in. (0.12 mm) or less with 0.002 in. (0.05 mm) metal foil being a preferred thickness for interior layers in many shield applications. In addition to the layers of metal foil, optional protective exterior layers of metal sheet on one or both sides of the shield structure can be included. The metal sheets have a thickness greater than 0.006 in. (0.15 mm) and up to about 0.050 in. (1.27 mm). The thickness of the optional exterior protective metal sheet is selected such that it can be formed and shaped as part of the unitary multilayer metal foil shield structure according to this invention. Preferably the protective exterior metal sheet layers will be between about 0.008 in. (0.20 mm) and about 0.030 in. (0.76 mm). In the multilayer metal foil structures of this invention, one or more layers of such metal sheets may be placed between the metal foil layers, if desired, for additional structural strength of the final unitary multilayer metal foil shield structure. For some shield applications the multilayer metal foil structure can be made entirely of metal foils having a thickness of 0.006 in. or less, without the use of any thicker metal sheet layers. The multilayer metal foil structures have surprising structural strength and rigidity when forge formed according to this invention.
The multilayer metal foil shield structures according to this invention are shaped by a forming process which includes providing a preform of at least three layers of metal sheet, at least two of which layers are metal foil layers having a thickness of 0.006 in. (0.15 mm) or less, where the layers are spaced apart to provide gaps between the layers, forming the multilayer preform over a shaping mold whereby a first portion of the preform is held in position to maintain the spaced apart positions to maintain desired gaps between the layers, a second portion of the preform is placed under tensile stress to shape that second portion of the preform into ridges or corners to form the desired three dimensional form and a third portion of the preform is placed under compression to shape that third portion of the preform into a wall section positioned at an angle from the plane of the first portion and an edge section to interlock the layers together in that third portion. The second portion provides the transition from the first portion having spaced apart layers and the third portion having compressed, interlocked layers. The third portion comprises a wall section and an edge section. It is preferred that the layers be compressed and interlocked together in both the wall section and the edge section. However, in some configurations of the structures of this invention, the layers may be compressed and shaped to form the wall section, but the layers are not interlocked together in part or all of the wall section. But in such configurations, the layers are always compressed and interlocked together in the edge section where the layers are preferably folded, curled or rolled together at the edge to form a bead along the edge of the structure. The compressed portion provides three dimensional shape of the structure and imparts structural strength to the overall multilayer metal foil structure by folding or wrinkling the sheets of the preform into interlocking relationship in the third portion to form a unitary rigid multilayer metal foil structure. The forming operation, which simultaneously stretches the second portion and compresses the third portion of the multilayer metal foil preform into the final multilayer metal foil structure, imparts three dimensional rigidity and structural strength to the final formed multilayer metal foil structure, while also maintaining the spaced apart layers and the gaps between the layers in the first portion of the preform. The forming operation also interlocks the layers at an edge portion of the structure preferably by folding, curling or rolling the edge, e.g., forming a cylindrical bead along the edge of the multilayer structure.
The present invention provides a formed metal structure comprising at least three layers of metal sheet, at least two of which layers are metal foil layers having a thickness 0.006 in. (0.15 mm) or less, formed into a three dimensional unitary structure whereby in a portion of the structure the layers have gaps therebetween provided by spacers to hold the layers apart and in a portion of the structure the layers are interlocked and folded together to substantially eliminate gaps between the layers thereby providing the three dimensional structural strength of the final part. The multilayer metal foil structure is three dimensionally formed from a preform of a stack of said metal layers over a mold whereby portions of the layers are shaped under tensile stress and portions of the layers are shaped under compressive conditions to form the metal foil layers into interlocking folds, wrinkles or rolls, while portions of the layers are maintained in spaced apart relationship with gaps between the layers.
This invention provides multilayer metal foil structures which are free standing, three dimensionally stable or rigid structures, which may be assembled or installed as stand-alone products for heat shield or acoustical shield uses, particularly in automotive applications, without the requirement of a support pan, stamping, frame or other structural support member for the shield.
The present invention provides a method of forming a multilayer metal structure by providing a multilayer preform of a stack of at least three layers of metal sheet at least two of which layers are metal foil each having a thickness of 0.006 in. (0.15 mm) or less where the layers have gaps therebetween, and forming said multilayer preform over a rigid mold whereby in a portion of the preform the layers are maintained with gaps therebetween, in a portion of the preform the layers are placed under tensile stress to shape that portion of the preform into ridges or corners to form the desired three dimensional shape and in a portion of the preform the layers are placed under compression to shape a portion of the preform into a three dimensional shape to impart structural strength to the metal structure by substantially eliminating the gaps between the layers and by interlocking the layers together in that portion of the preform to form a multilayer metal foil unitary, structure.
The present invention further provides the formed and shaped multilayer metal structure as described above wherein the layers comprise three metal sheets each having a thickness greater than 0.006 in. (0.15 mm). Similarly, the present invention provides the method as described above for forming and shaping multilayer metal structures from a multilayer preform wherein the layers comprise three metal sheets each having a thickness greater than 0.006in. (0.15 mm). It is preferred in these aspects of this invention that the preform and the resulting formed and shaped structure comprise four to nine or more layers, while five to seven layers are preferred for many heat and sound shield applications.
In one most preferred aspect of this invention, multilayer metal sheet shield parts having three, four, five or more layers are formed from multilayer metal sheet preforms by a single stroke stamping operation which forms the multilayer preform into a three dimensional rigid shaped structure in which a portion of the final part has the layers in a spaced apart relationship, a portion of the part has at least some of the layers stretched or tensioned around corners or ridges shaped in the part, and a portion of the part has the layers compressed vertically and longitudinally and/or laterally and interlocked together, preferably in a curled, rolled or folded bead along one or more edges of the part. The shaping and interlocking the layers together in a single stamping stroke provides a very efficient method of making multilayer metal heat and acoustic shields to fit any desired end use application. In another most preferred aspect, at least one, and preferably two, three or more, layers of the single stroke stamped part is metal foil sheet having thickness of 0.006 in. or less, e.g., 0.005 in., 0.002 in., and 0.0008 in. The single stroke stamping operation can also include stamping into the part attach points or reinforced bolt or screw holes for assembling the part on its final intended use location, such as on a vehicle.
In another practice of the above preferred aspect of the invention, it may be desirable to first form the curled, rolled or folded bead along one or more edges of the multilayer metal preform before subjecting the preform to the single stroke stamping operation to form the final three dimensional rigid multilayer metal shield. In this practice of the invention the selected number of metal sheets are stacked and trimmed to the desired engineered shield shape then stamped to form the curled, rolled or folded bead along the edges to form a unitary multilayer metal beaded preform. The beaded preform is substantially flat in overall shape but contains areas in the shape where the layers are in the spaced apart relationship and edge areas where the layers are curled, rolled or folded into a bead. In forming this flat beaded preform the stack need not be trimmed before stamping. The initial stamping of the stack can perform the trimming to shape, forming the edge beads and punching, compressing or otherwise forming as many final or near final features desired in the final shaped shield, such as attach points, openings for fitting with other parts in the final assembly, e.g., on a vehicle. The substantially flat (or other desired preliminary shape) multilayer metal beaded preforms are then efficiently transported (due to minimal volume) to the final assembly location where they are then stamped into the final three dimensional structural shield shape desired for the final engineered part. The final stamping operation can merely provide shaping to the three dimensional shape by compressing some areas stretching or tensioning some areas while maintaining the spaced apart relationship of the layers in a portion of the part, or can also provide additional punching, cutting or other operation to form the final desired engineered part.
In another aspect of this invention fibrous, plastic, resin or other non-metal materials are encapsulated between two or more layers of the multilayer metal sheet structure. The non-metallic materials are preferably sealed in the structure by the entire edge and any internal edges being curled, rolled or folded bead to seal the materials between the layers. The non-metallic materials can extend into the bead edge area and be curled, rolled or folded along with the metal sheet layers, or those materials can be trimmed to fit up to but short of the bead.